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Capacity determines placement; bandwidth describes one aspect of data access. Both matter, but neither alone predicts complete application performance.
Two servers with equal memory can execute a model at different speeds. Core count is not necessarily the cause: organisation, data access and engine matter. Owners should describe configurations thoroughly, while funders should assess more than cost per gigabyte.
Separate capacity and transfer
Capacity describes how much data a resource holds. Bandwidth describes transfer under particular conditions. Individual access latency and concurrent processes add other dimensions.
This applies to RAM and accelerator memory without making them identical. More system RAM does not become fast local VRAM. Transfers between them require the complete execution path to be considered.
The vLLM CPU-backend requirements discuss environment and work placement, illustrating why one memory-capacity line cannot specify a reproducible launch.
Keep a complete equipment record
For CPU servers, record processors, sockets, installed memory and known connection configuration. For GPUs, state exact card, VRAM and interconnects rather than an aggregate resource sum.
AWS R8i specifications discuss platform and memory capabilities separately. Another party’s generation comparisons are not your application’s result. Use them to specify candidates, not forecast performance.
For cloud VMs, add size, CPU-allocation model and region. One family can contain different configurations.
Run two application tests
First use a small context and fixed request count. Then increase working set or concurrency within supported limits. Preserve latency, errors and memory consumption.
If added capacity removes placement errors, that is one finding. If data already fitted and speed barely changes, more capacity needs another justification.
Do not attribute every plateau to memory. Compute, scheduling, networking or input preparation may be responsible. Compare stage observations before deciding.
Test shared operation
Add background preparation or the owner’s normal tasks. A single-job test can miss host-resource competition. This matters for a server shared by schedule.
Record cache state and process placement. Restarting with another configuration can change results without hardware replacement. Preserve settings and repeat the original control.
Show a funding partner a specific constraint and verification method. “Fast memory” cannot decide between a new card, more RAM or tuning the existing server.
Record the measured constraints
Unknown organisation details can be clarified technically without buying components first.
Read RAM and VRAM and capacity planning.