Spinning disks are slow and SSDs (SSDs) are used to cost a digital arm and a leg. This led many people to stick to hard drives or buy Macs with low-capacity SSDs – such as 250 GB or 500 GB – because the next increase increased costs by many hundreds of dollars. (I’m sitting here with a 2017 iMac with a 1TB Fusion drive, so I’m one of you.)
If you have a hard drive on your Mac or a low-capacity SSD, you are probably tempted to update your system and add speed or capacity. And some of you may be tempted to trim the cost of that upgrade by using an SD card (usually in Micro SD format) inserted into the card slot present on generations of Macs before those that included USB-C or Thunderbolt 3.
I recommend against the SD card slot, tempting as it may be, unless you use a card for mostly static storage ̵
SD cards use the same flash memory chips as SSDs, but the way memory is packaged and managed is quite different. An SSD has a more sophisticated controller system designed to work with the limitations of flash memory, which wears out after a significant number of write operations. An SSD “levels” this usage so that nowhere is it written continuously or excessively. Smooth wear dramatically extends SSD life. Many drives offer optional “trim”, a feature in which the drive and and the operating system convey file deletion information that helps improve overall typing speed.
SSDs also have a distributed flash memory architecture that provides far faster speeds than SD cards. A high-end 1TB Lexar HD card marked 95 megabytes per second (MBps) for data reading and marked class 10, U3, V30 – three measures of performance – for about 30 MBps data writing is about $ 200 street price. An Other World Computing SSD that can be installed instead of existing SSDs in the latest generations of MacBook Pros with removable drives costs $ 329 for 1 TB – and has a nominal read speed of 3,282 MB / s and a write speed of 2,488 MB / s. Quite different.
By the way, even if you can’t replace the internal drive of a Mac mini or iMac, you can use an external SSD in a USB 3 or Thunderbolt 3-equipped enclosure. OWC offers a 1 TB Thunderbolt 3 SSD for just under $ 300. You can clone the boot volume of the remote drive, restart, and find that your computer has a new lease. While this is possible with a Mac laptop, it can be too stressful to ensure that the drive stays connected wherever you use it.
This Mac 911 article is an answer to a question from Macworld reader Marcella.
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