NV Cache
| Header Cell - Column 0 | 128 MB | 256 MB | 1 GB |
|---|---|---|---|
| H-HDD Firmware | ~ 10 MB | ~ 10 MB | ~ 24 MB |
| Write Cache | 32 MB | 32 MB | 32 MB |
| OEM Pinned Data | 15 MB | 79 MB | 463 MB |
| SuperFetch Data | Remainder | Remainder | Remainder |
Flash memory capacities of 50 MB to 2 TB are supported, but Microsoft recommends a figure between 128 MB and 1 GB. The more Flash memory you have on your H-HDD, the more application data can be pinned into it. This is particularly interesting for OEMs, who want certain programs to be available quickly at all times. All remaining capacity will be used for application caching and SuperFetch.
However, a lot of high-speed Flash memory is expensive. The Samsung drive, which we received, was equipped with 256 MB Flash memory to increase application launch performance. According to Samsung, this represents a good balance between cost and a nice ReadyDrive experience, and it is expected to somewhat match 7,200 RPM drive performance with a 5,400 RPM unit.
When configured in multiple channels, SLC Flash memory performance can outperform mechanical hard drives in any aspect, but these configurations are expensive - we expect the first hybrid hard drives to deliver sustained transfer rates of up to 30 MB/s for the Flash memory. While 2.5" hard drives exceed 50 MB/s, this is still more than enough, as Flash memory does not suffer from long access times.
Microsoft has minimum performance requirements for H-HDDs, and Vista will automatically determine a H-HDD's performance once detected.
| Scenario | Sustained throughput (MB/second) |
|---|---|
| 4 kb random reads to a file pinned in the NV cache | >4 |
| 4 kb random writes to a file pinned in the NV cache | >4 |
| 64 kb sequential reads to a file pinned in the NV cache | >16 |
| 64 kb sequential writes to a file pinned in the NV cache | >8 |
Source: "Windows PC Accelerators" paper by Microsoft.
