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Buying a Solid-State Drive: 20 Terms You Need to Know

 Buying a Solid-State Drive: 20 Terms You Need to Know

If you're shopping for a solid-state drive—whether as a new boot drive or as an access-speeding cache for an existing boot hard drive—you're likely tech-savvy enough to dig into the innnards of your desktop or laptop. Even so, a swarm of ever-evolving jargon buzzes around SSDs, and some of it is bewildering even to serious PC enthusiasts. Not only that, but not every spec that SSD vendors cite is necessarily meaningful when you're shopping.

It's hard to buy a bad SSD these days for general use, but first-time upgraders will need a bit of background knowledge to keep from overspending. Let us be your guide: Here's a 101-level primer to the language you need to speak SSD-savvy.

Firmware refers to the software "instruction set" stored in an SSD in non-volatile memory. In a nutshell, it governs the operation of the drive. Firmware in an SSD context is referred to by a version number, and is flash-upgradable, usually via a manufacturer utility. The firmware is typically tied to a specific make and model of controller, so updates to the firmware for a given SSD controller chip can often be implemented across multiple manufacturers' drives, as soon as each manufacturer packages the firmware update for its drives. Firmware upgrades are typically distributed via the support section of an SSD manufacturer's website.

A firmware update can address performance issues with a given drive. Also note that a drive that has been on the market for some time may have shipped with an earlier version of a given controller's firmware early on, and a newer one later, meaning that performance or stability can vary depending on which particular sample you buy.

SSD Caching
An SSD can be installed as a boot drive, with the option to install programs and data on it (depending on the capacity of the SSD and whether the system can accommodate a secondary "data" drive). You'll see the maximum speed benefit from a given SSD if it's used in this way. But a different mode in which SSDs are used is as cache memory, usually in a system with a platter hard drive set up as the boot drive. In this kind of arrangement, the system uses the SSD to temporarily store frequently accessed data (program files, large data files, parts of the OS) for faster access from the solid-state memory than from the platter drive. This is managed automatically via the system, usually via a technology such as Intel's SRT (explained a bit later).

SSD caching was sometimes implemented in Windows ultrabooks (in which an SSD boot drive or an SSD cache arrangement is a prerequisite). On desktops, an SSD cache can be implemented using a low-capacity, conventional SATA SSD in the 2.5-inch form factor or, in some older implementations, via an mSATA SSD module. A newer version of this technique is Intel's Optane Memory technology, which we'll get to later in this story.

Serial ATA
Serial ATA, often abbreviated to SATA, has for some time been the standard bus interface for drives inside consumer and business PCs. It's employed by hard drives, SSDs, and optical drives alike. And while SSDs do come in other interfaces and designs (especially M.2; see below), the SATA SSD in its 2.5-inch form factor is the most familiar to upgraders.

A typical 2.5-inch SSD with a physical SATA interface will have both a SATA data connector (which connects, in a desktop, to one of the SATA ports on the motherboard) and a wider, blade-like "SATA-style" power connector (which connects to a SATA power lead coming from the power supply). Inside a laptop, these connectors on the drive usually engage with a hardwired connection or a very short ribbon cable with both connectors on it.

The SATA data (left) and power (right) connectors on an SSD

The SATA data (left) and power (right) connectors on an SSD.

The SATA interface also describes the nature of the data bus that the SSD uses, which is why some M.2 drives (which use a wholly different physical connector; more on them below) actually route their data over the SATA bus. SATA itself has speed grades, and the ones you'll see in any SSDs you're considering are SATA 2 and SATA 3, variously called "SATA II"/"SATA 3Gbps" or "SATA III"/"SATA 6Gbps," respectively. These indicate the maximum data transfer rate possible with the drive, assuming it's installed in a PC with a SATA interface supporting the same standard.

In current SATA-bus drives, SATA III/SATA 6Gbps is the standard; we mention this in the event you're shopping older, second-hand, or remaindered drives that might be 3Gbps only. To gain the maximum throughput benefit of SATA 6Gbps, a 6Gbps SSD must be connected to a 6Gbps-compatible SATA port. Connected to a SATA II port, it will work, but the maximum data transfer rate will be constrained to 3Gbps. This will only be an issue to watch for when upgrading an older PC.

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