DGX H100 Specs Mastery

Every number you need, why it is what it is, and how exam distractors try to trick you.

1. Warm-up: how much network bandwidth leaves one DGX H100?

A capacity planner asks: "What's the peak bandwidth one DGX H100 can push to the rest of the cluster?" Below are four answers people often give. Only one holds up.

WRONG"Eight 200 Gb/s ConnectX-6 ports, so about 400 GB/s"

This mixes in the wrong generation. ConnectX-6 at 200 Gb/s (HDR) belongs to the DGX A100. The DGX H100 uses ConnectX-7 at 400 Gb/s (NDR). The arithmetic is also wrong: 8 × 200 Gb/s = 1,600 Gb/s = 200 GB/s, not 400 GB/s.

WRONG"7.2 TB/s, because NVSwitch extends between nodes"

7.2 TB/s is a real DGX H100 number, but it's the NVSwitch GPU-to-GPU bandwidth inside the node. It's the right number for the wrong question. Inter-node traffic leaves the box through the network adapters.

CORRECT"About 1 TB/s bidirectional, from ten 400 Gb/s ConnectX-7 ports"

10 × 400 Gb/s = 4,000 Gb/s = 500 GB/s each direction, which is 1 TB/s bidirectional. This is NVIDIA's headline datasheet figure.

WRONG"Count the four OSFP cages on the back: 4 × 400 Gb/s = 200 GB/s"

This miscounts the 4 OSFP cages on the back of the DGX H100. Those 4 physical cages carry 8 ConnectX-7 400 Gb/s ports (two per cage), not 4 adapters.

Three things decide this: the generation (ConnectX-7 / 400 Gb/s, not ConnectX-6 / 200 Gb/s), where the bandwidth applies (NVSwitch is inside the node, the NICs go between nodes), and the units (Gb/s → GB/s, one-way → bidirectional). This lesson trains all three.

2. Units first: the three traps behind most spec questions

Trap 1: bits (Gb) vs bytes (GB)

Network speeds are quoted in gigabits per second (Gb/s, small b). Memory and NVLink bandwidth are quoted in gigabytes per second (GB/s, big B). 1 byte = 8 bits.

400 Gb/s ÷ 8 = 50 GB/s

Trap 2: one direction vs bidirectional

A link can send and receive at full speed at the same time. Marketing figures often add both directions together ("bidirectional"), which doubles the number.

LinkPer directionBidirectional (both added)
One ConnectX-7 port400 Gb/s = 50 GB/s800 Gb/s = 100 GB/s
One H100's NVLink450 GB/s900 GB/s (headline)
All 10 ConnectX-7 in a DGX H100500 GB/s1 TB/s (headline)

Trap 3: per GPU vs per node, and which network

ScopeExample
Per GPUNVLink 900 GB/s · one compute NIC 400 Gb/s · HBM3 3.35 TB/s
Per node, intra-nodeNVSwitch total 7.2 TB/s (8 × 900 GB/s)
Per node, compute fabric only8 × 400 Gb/s = 3.2 Tb/s = 400 GB/s per direction (800 GB/s bidirectional)
Per node, all network adapters10 × 400 Gb/s = 4 Tb/s = 500 GB/s per direction (1 TB/s bidirectional)
"Small b is for the cable, big B is for the chip." Network = bits. Memory and NVLink = bytes. To go from bits to bytes, divide by 8. For "bidirectional," double it.

3. DGX H100 at a glance: the 10 numbers to memorize

8
H100 SXM5 GPUs
640 GB
total GPU memory (8 × 80 GB HBM3)
4
4th-gen NVSwitch chips
7.2 TB/s
NVSwitch GPU-to-GPU bandwidth (bidirectional)
900 GB/s
NVLink per GPU (bidirectional, 18 links)
10
ConnectX-7 400 Gb/s network adapters
1 TB/s
peak bidirectional network bandwidth
32 PFLOPS
FP8 AI performance (with sparsity)
2 TB
system RAM · 2× Xeon 8480C, 112 cores
~10.2 kW
max power · 8U chassis

Plus storage: 2 × 1.92 TB NVMe M.2 (OS) and 8 × 3.84 TB NVMe U.2 (≈ 30 TB internal data).

4. Inside the box: a guided tour

DGX H100 (8U) H100H100H100H100 H100H100H100H100 80GB HBM380GB HBM380GB HBM380GB HBM3 80GB HBM380GB HBM380GB HBM380GB HBM3 4 × NVSwitch (4th gen) · 7.2 TB/s total · each GPU 900 GB/s via 18 NVLinks INTRA-node only: GPU ↔ GPU inside this box PCIe Gen5 switches: each GPU paired with its own NIC (GPU i ↔ NIC i) 8 × ConnectX-7 single-port 400 Gb/s (compute fabric) exposed through 4 OSFP twin-port cages · 3.2 Tb/s = 400 GB/s each way 2 × dual-port ConnectX-7 storage / in-band · up to 400 Gb/s 2 × Intel Xeon Platinum 8480C 112 cores total · 2 TB RAM NVMe OS: 2 × 1.92 TB M.2 (RAID 1) Data: 8 × 3.84 TB U.2 (~30 TB, /raid) Management 10 GbE onboard NIC · BMC (RJ45) ~10.2 kW max · 6 PSUs

5. The H100 GPU itself (SXM5 version, as used in DGX)

SpecValueNotes
ArchitectureHopperSuccessor to Ampere (A100), predecessor to Blackwell (B200)
Form factorSXM5A socketed module on the baseboard (not a PCIe card). Enables full NVLink.
GPU memory80 GB HBM3Per GPU
Memory bandwidth3.35 TB/sGPU ↔ its own HBM3, the fastest link in the system
NVLink900 GB/s4th-gen NVLink, 18 links, bidirectional
PCIeGen5 x16~128 GB/s bidirectional (~64 GB/s each way)
Max power (TDP)up to 700 WPer GPU
FP8 Tensor~3,958 TFLOPS*≈ 4 PFLOPS, so × 8 GPUs ≈ 32 PFLOPS per DGX
BF16 / FP16 Tensor~1,979 TFLOPS*Training precision
TF32 Tensor~989 TFLOPS*
FP64 / FP64 Tensor34 / 67 TFLOPSHPC precision
MIGup to 7 instancese.g. 7 × 1g.10gb
Key features4th-gen Tensor Cores, Transformer Engine (dynamic FP8/FP16), DPX instructions, confidential computing, NVLink SHARP (NVLS) with NVSwitch

* Tensor figures marked with an asterisk are NVIDIA's "with sparsity" peaks. Dense is half.

The H100 PCIe card is a different product: 80 GB HBM2e, ~2 TB/s, 350 W, NVLink only through a bridge. DGX H100 uses SXM5. If an answer quotes PCIe-card specs for a DGX, it's a distractor.
"4 switches, 18 links, 900 per GPU, 7.2 per box." Check: 18 × 50 = 900 and 8 × 900 = 7,200 GB/s = 7.2 TB/s.
In a standard DGX H100 cluster, NVSwitch bandwidth does not extend across nodes. Answers like "extend the NVSwitch fabric across nodes" or "inter-node NVLink at 7.2 TB/s" are distractors. (Products like GH200 NVL32 / GB200 NVL72 use external NVLink Switch systems, but that's not a DGX H100 BasePOD.)

7. Inter-node: the 10 ConnectX-7 adapters

GroupCountSpeedPurposePhysical ports
Compute fabric8 × single-port ConnectX-7400 Gb/s each (NDR InfiniBand or Ethernet)GPU ↔ GPU between nodes (NCCL), one per GPU, rail-optimized4 OSFP twin-port cages (2 × 400G each)
Storage / in-band2 × dual-port ConnectX-7up to 400 Gb/sStorage fabric and in-band management networksQSFP112 ports
ManagementOnboard NIC + BMC10 GbE + 1 GbE BMCAdmin, out-of-bandRJ45

Doing the arithmetic

WhatCalculationResult
Per compute NIC (per GPU)400 Gb/s ÷ 850 GB/s each way
Compute fabric per node8 × 400 Gb/s = 3.2 Tb/s ÷ 8400 GB/s each way · 800 GB/s bidirectional
All 10 adapters (headline)10 × 400 Gb/s = 4 Tb/s ÷ 8 = 500 GB/s each way × 21 TB/s peak bidirectional
When a question asks for the "total peak network bandwidth of a DGX H100," the expected answer is NVIDIA's datasheet figure: 10 × ConnectX-7 400 Gb/s → 1 TB/s peak bidirectional. When it asks about GPU-to-GPU compute fabric bandwidth specifically, think 8 × 400 Gb/s = 3.2 Tb/s (400 GB/s each way).
"Ten NICs, four hundred each, one terabyte both ways." And "8 for GPUs, 2 for storage."

8. The bandwidth ladder: every link from fastest to slowest

This ladder explains much of distributed-training design: keep the most communication-heavy work on the fastest links.

#LinkBandwidthPer direction (GB/s)
1H100 ↔ its own HBM3 memory3.35 TB/s(memory bandwidth)
2NVSwitch total inside one DGX7.2 TB/s bidir3,600 total
3One GPU's NVLink900 GB/s bidir450
4All 10 NICs of one DGX1 TB/s bidir500
5Compute fabric of one DGX (8 NICs)3.2 Tb/s400
6One GPU's PCIe Gen5 x16~128 GB/s bidir~64
7One GPU's compute NIC400 Gb/s50
Per GPU, NVLink (450 GB/s each way) is about 9× faster than its network NIC (50 GB/s). That's why tensor parallelism stays inside a node (on NVLink), while data and pipeline parallelism span nodes (over InfiniBand).
HBM is the desk you work at. NVLink is the hallway to colleagues on your floor. InfiniBand is the road to other buildings. PCIe is the stairwell to the basement. You keep the chattiest teams on the same floor.

9. Storage: NVMe drives

DrivesCapacityTypical configPurpose
2 × NVMe M.21.92 TB eachRAID 1 (mirror)Operating system
8 × NVMe U.23.84 TB each = 30.72 TB (~30 TB)RAID 0 (stripe), mounted at /raidLocal data cache / scratch: datasets, temporary checkpoints
"2 small for the OS, 8 big for the data." 1.92 × 2 (mirror) and 3.84 × 8 ≈ 30 TB. The data drives match the GPU count: 8 GPUs, 8 NICs, 8 data NVMe.

10. CPU, memory, power, size

SpecDGX H100
CPUs2 × Intel Xeon Platinum 8480C (Sapphire Rapids), 112 cores total (56 each), 2.0 GHz base, up to 3.8 GHz boost
System memory2 TB DDR5
Max power~10.2 kW
Rack units8U
Weight~130 kg (~287 lb)
Operating temperature5–30 °C (41–86 °F)
SoftwareDGX OS (Ubuntu-based) or Red Hat Enterprise Linux; NVIDIA AI Enterprise; Base Command (BCM for cluster management)
10.2 kW per node is a big rack-planning number. Many data-center racks are designed for far less, so DGX H100 deployments often have only a few nodes per rack, or need high-density power and cooling.

11. DGX A100 vs H100 vs H200: spotting the wrong generation

Exams love borrowing a number from the neighboring generation. Learn the pattern of each.

SpecDGX A100DGX H100DGX H200
GPU architectureAmpereHopperHopper
GPUs8 × A1008 × H1008 × H200
Memory per GPU40 or 80 GB (HBM2 / HBM2e)80 GB HBM3141 GB HBM3e
Total GPU memory320 or 640 GB640 GB1,128 GB
Memory bandwidth per GPU~1.6–2.0 TB/s3.35 TB/s4.8 TB/s
NVLink per GPU600 GB/s (NVLink 3, 12 links)900 GB/s (NVLink 4, 18 links)900 GB/s
NVSwitch6 × 2nd-gen, 4.8 TB/s4 × 4th-gen, 7.2 TB/s4 × 4th-gen, 7.2 TB/s
Compute NICs8 × ConnectX-6 200 Gb/s (HDR)8 × ConnectX-7 400 Gb/s (NDR)8 × ConnectX-7 400 Gb/s
Storage/in-band NICs2 × dual-port ConnectX-62 × dual-port ConnectX-72 × dual-port ConnectX-7
Headline network-1 TB/s peak bidirectional1 TB/s
CPUs2 × AMD EPYC 7742 (128 cores)2 × Intel Xeon 8480C (112 cores)2 × Intel Xeon 8480C
System RAM1 TB or 2 TB2 TB2 TB
AI performance5 PFLOPS (FP16, sparse)32 PFLOPS FP832 PFLOPS FP8
Max power~6.5 kW~10.2 kW~10.2 kW
Size6U8U8U
Generation fingerprints:
A100 era = ConnectX-6, 200 Gb/s, NVLink 600, 6 NVSwitches, 4.8 TB/s, AMD EPYC, 6U.
H100 era = ConnectX-7, 400 Gb/s, NVLink 900, 4 NVSwitches, 7.2 TB/s, Intel Xeon, 8U.
H200 = the H100 box with bigger, faster memory (141 GB HBM3e, 4.8 TB/s).
"4.8 TB/s" appears twice: as the DGX A100's NVSwitch total and as the H200's per-GPU memory bandwidth. Read what the number is attached to.

12. BasePOD and SuperPOD context

DGX H100 nodes are the building block of NVIDIA's reference architectures. The spec-level facts to tie to this guide:

BasePOD vs SuperPOD, the four networks, leaf/spine/cable counts per SU, rack power limits, and a sizing calculator are in the AI factory architecture guide (reference architectures, sizing math).

13. Expected vs achieved bandwidth (what tests really show)

TestTheoreticalHealthy measured (roughly)
Single-node NCCL AllReduce busbw (8 GPUs over NVLink)450 GB/s per GPU each way~450+ GB/s; can be higher with NVLS
Multi-node NCCL AllReduce busbw (8 × 400G per node)400 GB/s per node each way~350–400 GB/s for large messages
ib_write_bw on one NDR link400 Gb/sClose to line rate (high 300s Gb/s)
HBM3 memory bandwidth3.35 TB/sA large fraction of peak in bandwidth tests

Measured values vary with software versions and message sizes. Exams generally test theoretical datasheet values, and troubleshooting questions test "far below expected."

14. Unit converter

Try: 10 × 400 Gb/s (the DGX H100 headline) · 8 × 400 Gb/s (compute fabric) · 8 × 200 Gb/s (DGX A100 compute) · 8 × 900 GB/s bidirectional (NVSwitch total).

15. All memory hooks on one page

16. Sample outputs

What the commands in this guide print. Expand a command to see a typical result and what to check in it.

Illustrative output, not captured from a real system. Hostnames, serial numbers, GUIDs, MAC and IP addresses are invented, and columns and wording vary between versions. Learn the shape of each output and the fields called out under it.
nvidia-smi topo -mConfirm NV18 between all GPU pairs
        GPU0  GPU1  GPU2  GPU3  GPU4  GPU5  GPU6  GPU7  NIC0  NIC1  NIC2  NIC3  NIC4  NIC5  NIC6  NIC7  NIC8  NIC9  NIC10 NIC11 CPU Affinity      NUMA Affinity  GPU NUMA ID
GPU0     X    NV18  NV18  NV18  NV18  NV18  NV18  NV18  PIX   NODE  NODE  NODE  NODE  NODE  SYS   SYS   SYS   SYS   SYS   SYS   0-55,112-167      0              N/A
GPU1    NV18   X    NV18  NV18  NV18  NV18  NV18  NV18  NODE  NODE  NODE  PIX   NODE  NODE  SYS   SYS   SYS   SYS   SYS   SYS   0-55,112-167      0              N/A
GPU2    NV18  NV18   X    NV18  NV18  NV18  NV18  NV18  NODE  NODE  NODE  NODE  PIX   NODE  SYS   SYS   SYS   SYS   SYS   SYS   0-55,112-167      0              N/A
GPU3    NV18  NV18  NV18   X    NV18  NV18  NV18  NV18  NODE  NODE  NODE  NODE  NODE  PIX   SYS   SYS   SYS   SYS   SYS   SYS   0-55,112-167      0              N/A
GPU4    NV18  NV18  NV18  NV18   X    NV18  NV18  NV18  SYS   SYS   SYS   SYS   SYS   SYS   PIX   NODE  NODE  NODE  NODE  NODE  56-111,168-223    1              N/A
GPU5    NV18  NV18  NV18  NV18  NV18   X    NV18  NV18  SYS   SYS   SYS   SYS   SYS   SYS   NODE  NODE  NODE  PIX   NODE  NODE  56-111,168-223    1              N/A
GPU6    NV18  NV18  NV18  NV18  NV18  NV18   X    NV18  SYS   SYS   SYS   SYS   SYS   SYS   NODE  NODE  NODE  NODE  PIX   NODE  56-111,168-223    1              N/A
GPU7    NV18  NV18  NV18  NV18  NV18  NV18  NV18   X    SYS   SYS   SYS   SYS   SYS   SYS   NODE  NODE  NODE  NODE  NODE  PIX   56-111,168-223    1              N/A
(NIC0-NIC11 rows trimmed)

Legend:

  X    = Self
  SYS  = Connection traversing PCIe as well as the SMP interconnect between NUMA nodes (e.g., QPI/UPI)
  NODE = Connection traversing PCIe as well as the interconnect between PCIe Host Bridges within a NUMA node
  PHB  = Connection traversing PCIe as well as a PCIe Host Bridge (typically the CPU)
  PXB  = Connection traversing multiple PCIe bridges (without traversing the PCIe Host Bridge)
  PIX  = Connection traversing at most a single PCIe bridge
  NV#  = Connection traversing a bonded set of # NVLinks

NIC Legend:

  NIC0: mlx5_0
  NIC1: mlx5_1
  NIC2: mlx5_2
  NIC3: mlx5_3
  NIC4: mlx5_4
  NIC5: mlx5_5
  NIC6: mlx5_6
  NIC7: mlx5_7
  NIC8: mlx5_8
  NIC9: mlx5_9
  NIC10: mlx5_10
  NIC11: mlx5_11

What to look at: This is how the spec shows up on a real node: every GPU pair reads NV18 (18 NVLink 4 links through the 4 NVSwitches, 900 GB/s per GPU), and each GPU has one PIX NIC, which is its own 400 Gb/s ConnectX-7 compute port. The 12 NIC entries are the 8 compute ports plus the 4 ports of the 2 dual-port storage adapters; a GPU pair showing SYS or a lower NV count means NVLink is not fully up.

ib_write_bw -d mlx5_0 --report_gbits dgx02RDMA write bandwidth on one NDR link
---------------------------------------------------------------------------------------
                    RDMA_Write BW Test
 Dual-port       : OFF          Device         : mlx5_0
 Number of qps   : 1            Transport type : IB
 Connection type : RC           Using SRQ      : OFF
 PCIe relax order: ON
 ibv_wr* API     : ON
 TX depth        : 128
 CQ Moderation   : 1
 Mtu             : 4096[B]
 Link type       : IB
 Max inline data : 0[B]
 rdma_cm QPs     : OFF
 Data ex. method : Ethernet
---------------------------------------------------------------------------------------
 local address: LID 0x11 QPN 0x0123 PSN 0x1a2b3c RKey 0x1fff00 VAddr 0x007f2a00000000
 remote address: LID 0x12 QPN 0x0456 PSN 0x4d5e6f RKey 0x2fff00 VAddr 0x007f3b00000000
---------------------------------------------------------------------------------------
 #bytes     #iterations    BW peak[Gb/sec]    BW average[Gb/sec]   MsgRate[Mpps]
 65536      5000             391.85             391.72               0.747146
---------------------------------------------------------------------------------------

What to look at: The client run against a server already listening on dgx02 reports about 392 Gb/s, close to the 400 Gb/s NDR line rate of one ConnectX-7 port, which is about 50 GB/s each way. A result near 200 Gb/s suggests the link trained at HDR or half width, and far lower numbers point to cabling, PCIe placement, or a congested fabric; without --report_gbits the same figures appear in MB/sec.

all_reduce_perf -b 8 -e 8G -f 2 -g 8Single-node NCCL AllReduce over NVLink
# nThread 1 nGpus 8 minBytes 8 maxBytes 8589934592 step: 2(factor) warmup iters: 5 iters: 20 agg iters: 1 validation: 1 graph: 0
#
# Using devices
#  Rank  0 Group  0 Pid  51234 on      dgx01 device  0 [0x18] NVIDIA H100 80GB HBM3
#  Rank  1 Group  0 Pid  51234 on      dgx01 device  1 [0x2a] NVIDIA H100 80GB HBM3
#  Rank  2 Group  0 Pid  51234 on      dgx01 device  2 [0x3a] NVIDIA H100 80GB HBM3
#  Rank  3 Group  0 Pid  51234 on      dgx01 device  3 [0x5d] NVIDIA H100 80GB HBM3
#  Rank  4 Group  0 Pid  51234 on      dgx01 device  4 [0x9a] NVIDIA H100 80GB HBM3
#  Rank  5 Group  0 Pid  51234 on      dgx01 device  5 [0xab] NVIDIA H100 80GB HBM3
#  Rank  6 Group  0 Pid  51234 on      dgx01 device  6 [0xba] NVIDIA H100 80GB HBM3
#  Rank  7 Group  0 Pid  51234 on      dgx01 device  7 [0xdb] NVIDIA H100 80GB HBM3
#
#                                                              out-of-place                       in-place          
#       size         count      type   redop    root     time   algbw   busbw #wrong     time   algbw   busbw #wrong
#        (B)    (elements)                               (us)  (GB/s)  (GB/s)            (us)  (GB/s)  (GB/s)       
           8             2     float     sum      -1    30.21    0.00    0.00      0    29.87    0.00    0.00      0
   ...
     1048576        262144     float     sum      -1    30.50   34.38   60.16      0    30.12   34.81   60.93      0
   ...
   134217728      33554432     float     sum      -1    620.0  216.48  378.84      0    618.4  217.04  379.82      0
   ...
  1073741824     268435456     float     sum      -1   4100.0  261.89  458.30      0   4096.2  262.13  458.73      0
   ...
  4294967296    1073741824     float     sum      -1    16000  268.44  469.76      0    15987  268.65  470.14      0
  8589934592    2147483648     float     sum      -1    31400  273.56  478.74      0    31386  273.69  478.96      0
# Out of bounds values : 0 OK
# Avg bus bandwidth    : 152.418 
#

What to look at: Read the busbw column for the largest messages: about 479 GB/s at 8 GB matches the guide's healthy single-node figure of roughly 450 GB/s or more over NVLink (higher with NVLS). A large-message busbw near 50 GB/s means traffic is falling back to PCIe or the network instead of NVLink, and any nonzero #wrong value means corrupted results.

df -h /raidCheck the local NVMe data RAID
Filesystem      Size  Used Avail Use% Mounted on
/dev/md1         28T  1.2T   27T   5% /raid

What to look at: The 8 x 3.84 TB U.2 drives in RAID 0 total 30.72 TB, which df -h shows as 28T because it counts in binary units (TiB). A size near 3.5T would mean only one data drive is in the array, and a missing /raid mount means the data RAID was not assembled at boot; remember that it is scratch with no redundancy.

17. Distractor patterns

  1. Wrong generation: ConnectX-6, 200 Gb/s, HDR, NVLink 600 GB/s, 6 NVSwitches, AMD EPYC, 4.8 TB/s NVSwitch → that's DGX A100.
  2. Wrong scope: 7.2 TB/s (NVSwitch, intra-node) offered as network bandwidth. 900 GB/s (per GPU) offered as per-node.
  3. Wrong units: "400 GB/s per NIC" (it's 400 Gb/s = 50 GB/s). Mixing up Tb/s and TB/s.
  4. Wrong direction: 500 GB/s (one way) vs 1 TB/s (bidirectional). Read whether the question says "bidirectional."
  5. Wrong count: "4 ConnectX-7" (confusing the 4 OSFP cages with 8 ports), "8 NICs total" (forgetting the 2 storage adapters).
  6. Wrong form factor: H100 PCIe specs (HBM2e, 2 TB/s, 350 W) for a DGX (SXM5: HBM3, 3.35 TB/s, 700 W).
  7. Wrong memory: 141 GB / HBM3e / 4.8 TB/s per GPU → that's H200.
  8. "Extend NVSwitch across nodes" in a DGX H100 BasePOD → no. Inter-node traffic uses InfiniBand.
  9. Sparse vs dense FLOPS: 32 PF FP8 is the sparse figure. Dense is about 16 PF.

18. Flashcards (click to flip)

19. Practice quiz (25 questions)

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