I have some doubts. For example, why do you want 30apr2005, if 28feb2005 is closer to 28mar2005? I'm not sure what you mean by 'In case of indifference between n observations.' , so I've interpreted freely.
Solid state disks (SSD) are an entirely electronic alternative to your standard SATA hard disk drive (HDD). SSD uses flash memory chips to store your data, as opposed to the head and spinning platter configuration of your current HDD hard drive. While the cost per gigabyte for an SSD drive is too costly for standard consumer use in 2011, the SSD is definitely the next step in hard drive technology.
Boot Speed
When you first turn on your computer, the hard drive takes a second to spin up before it can read the drive and start booting. This leads to a significantly lower boot speed than SSD, which starts the second power hits the drive. In testing done for Computer World, Lucas Mearian found that his SSD booted Windows XP in 20 seconds, while his HDD took 40 seconds.
Read/Write Speeds
The SDD has the advantage in read/write speeds -- period. Your average SSD advertises 250 MB per second read speeds and 100 MB per second write speeds. In testing, this holds true depending on your brand of SSD and HDD. Bear in mind, of couse, that speeds vary depending on your brand of drive. Also, speeds drop over time; as you fill and use your drive, you'll likely notice a much slower read/write speed.
Durability
Because an SSD features no moving parts it's more durable and extremely klutz-friendly -- which is why it's used primarily in mobile devices. An SSD isn't susceptible to magnets, vibration or drops. They also produce less heat, which is better for the heat-sensitive components of your computer. This durability makes SSD a practical decision for users on the road or in high-impact environments where damage to an HDD is more likely.
Resource Use
One of the main claims to SSD's superiority is that they use fewer computer resources, including battery life. In Mearian's tests for Computer World, he found that battery life was only extended by five minutes when the SSD was in use. The SATA drive's random access time was 17 milliseconds -- significantly longer than the SSD, which clocked in well under one millisecond. However, the SSD uses more CPU than HDD.
Endurance
While SSD drives are in most ways superior to HDD, they may present a lower endurance over time and more likely rate of failure than your standard SATA HDD. Which is to say: hard drives fail. It's a fact of life. The kind of SSD you're likely to buy on the consumer market has a highly variably lifespan: anywhere from 2,000 to 10,000 write/erase cycles. AN SSD's lifespan is highly variable to the type of drive you purchase, measurements the manufacturer uses to increase lifespan and how you use the drive.
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If you've been paying attention to the ports on new PC and Mac desktops and laptops, you'll see that just about all of them come with 'new, faster' USB 3.0 ports. These ports are usually (but not always) colored blue to differentiate them from older, slower USB 2.0 ports. Then there's the professional-class eSATA port found on performance PCs, which is physically incompatible with USB, but is still found on desktop replacement laptops and on tower desktops. At home and in the office, which would I use and why?
The Universal Serial Bus (USB) interface is ubiquitous. It began to come standard on Toshiba laptops and Apple desktops in the late 1990s; now just about every system comes with at least one USB port so it can connect to peripherals like printers, mice, keyboards, external hard drives, scanners, and the like. USB 1.1 started the ball rolling, but is really only useful for communicating with printers, mice, and keyboards. Once USB 2.0 took off in the 2000s, you could start connecting peripherals that stored data like digital media players, USB flash keys, and external hard drives. USB 2.0 tops out at 480Mbps, glacial compared to the 5 Gbps of USB 3.0. You'll never get exactly that 5Gbps throughput, since a) it's shared among the multiple ports connected to the same USB host controller, and b) many devices themselves aren't capable of reaching that level of throughput (spinning hard drives are a prime example). That said, USB's commonaility make it the go-to interface over more esoteric interfaces like eSATA, Fibre Channel, and Thunderbolt.
eSATA has always been considered a professional interface when compared with USB. Seen in systems like professional workstations and graphics artists' high-end PCs, eSATA has the benefit of being designed to work with hard drives primarily, while USB needs to be compatible with many other functions (mouse, keyboard, audio interface, charging, etc.). You'll find it was the 'fastest' throughput interface (1.5 Gbps to 6 Gbps) on most PCs before the advent of USB 3.0 and Thunderbolt (10 Gbps). Each eSATA device connects on a one-to-one basis with the PC, so you're not sharing the signal via an internal or external hub. That way the PC's motherboard chipset only has to deal with one drive at a time, and not with multiple devices simultaneously, as with USB. Before USB 3.0, powered eSATA (aka, eSATA+USB 2.0) was the way to get a fast portable drive working with a laptop without having to use a power adapter for the drive.
eSATA still has its place: IT managers can control the use of external hard drives and USB sticks by disabling USB ports on client PCs, while still supporting external drives for the people that need them by using eSATA. eSATA interfaces are also much more common on cable and fiber TV DVRs at home, so you can expand your storage easily with an eSATA drive.
So which do you use? If you're concerned about conveying your data from PC to PC, then USB 3.0 is the undoubted winner. Even if the PC or Mac you're connecting to has older USB 1.1 or USB 2.0 ports, the peripheral will at least connect and transfer data, albeit at a slower rate. If you are concerned about storage alone, particularly for work projects connecting to a single PC, then eSATA is a totally valid choice. You may even find it faster than USB if you have a lot of other USB devices connected to the PC at the same time.