AS SSD Access Time Explained: Reading the Acc.time Row
The last row of the AS SSD Benchmark grid, Acc.time, is the easiest to overlook and the only one where a smaller number wins. It reports access time — latency — in milliseconds, separately for reading and writing. Throughput rows tell you how fast data flows once the drive gets going; access time tells you how long the drive takes to get going at all. This page explains how each of the two figures is measured, why they differ, and how to judge the numbers on your own result. Run the benchmark from our download page to follow along.
How the read access time is measured
Read access time in AS SSD is determined across the entire capacity of the drive — a full-stroke measurement, as the tool’s official description (carried by TweakTown’s review archive and the major download sites) puts it. The benchmark requests data from positions spanning the whole drive rather than from one convenient corner, so the figure represents the average time to begin reading from anywhere, not from the fastest neighbourhood. That makes the read figure a conservative, whole-drive latency measure: a drive cannot flatter it by being quick only in one region.
How the write access time is measured
Write access time is measured using the 1 GB test file — the same default test size the main synthetic tests use. It captures how long the drive takes to begin and complete write accesses against that file. Because the two directions are measured differently — full-capacity reads versus a 1 GB write pattern — the read and write figures are not two readings of one quantity. Treat them as two separate diagnostics, each meaningful on its own terms, and expect them to differ.
Why write access time is usually the larger number
On most results you will ever see, the write figure exceeds the read figure, sometimes by a wide margin. The reason is structural. Reading flash is a lookup: the controller translates an address and returns the stored charge state. Writing flash is a programme operation, potentially preceded by block management work inside the drive, and on a busy or nearly full drive it can involve the controller shuffling existing data out of the way first. Caching hides much of this on a healthy drive with free space, which is why the write figure is also a useful canary: when it balloons relative to the same drive’s earlier results, the drive’s free space, cache behaviour or background state has changed. A sourced example below shows a completely typical gap.
A real example, with its source
In its review of the Lexar NQ100 240 GB, a DRAM-less SATA drive, Assistouest Informatique published a full AS SSD row set: sequential speeds of 510 MB/s read and 323 MB/s write, 4K results of 18 MB/s read and 57 MB/s write, 4K-64Thrd results of 53 MB/s read and 132 MB/s write — and access times of 0.05 ms read and 0.64 ms write. Two lessons sit in that pair of numbers. First, the write access time is more than twelve times the read figure on an ordinary, healthy budget drive; a gap like that is normal, not a fault. Second, even the “slow” figure here is a fraction of a millisecond — the review itself notes these access times as excellent next to a mechanical drive, which is the context that matters: access time is where the felt difference between flash and spinning media lives, far more than in any throughput row.
How access time relates to the other rows
Access time and the 4K row are two views of the same underlying quality. A drive that begins each small access quickly posts both a low Acc.time and a strong 4K result; a drive with poor small-access latency is weak in both. Access time is not, however, an input to the total score — the simplified score formula is built from the Seq, 4K and 4K-64Thrd rows only — so treat Acc.time as diagnostic evidence rather than a scoring component. It is also unit-sensitive: AS SSD always shows this row in milliseconds, even when you switch the speed rows to IOPS with the View menu (see MB/s vs IOPS explained), because latency is a time, not a rate.
Reading your own Acc.time result
Judge the row in three passes. Direction: lower is better, in both columns — the only row in the grid where that is true. Proportion: compare the read/write gap with published results for your drive or its class rather than expecting the two to match; a wide gap is typical, and the Lexar example above shows how wide “typical” can be. Change over time: the most valuable use of this row is longitudinal — re-run the benchmark periodically under the same conditions (same version, same test size, similar free space) and watch for drift, especially in the write figure, which reacts first to a filling drive. If a single row has to summarise why an SSD feels instant, it is this one — and now you know exactly how both halves of it are measured. For the rest of the grid, see how to read AS SSD scores.
A note on comparing access times with reviews
One frustration to expect: many reviews print the speed rows and the total but leave access times inside their screenshot rather than their text, so a like-for-like published Acc.time for your exact drive can be hard to find. That is a gap in the reviews, not in your result. The Lexar example above is valuable precisely because the reviewer stated both figures in words. Where no sourced figure exists for your drive, fall back on the longitudinal method — your own earlier runs, under identical settings, are the most honest baseline an access time can have.