The 4TB model has very fast access time, that is why it makes audible seek noises when accessing lots of small files. Both of my 4TB drives measured just under 12ms in random access performance. This - not linear transfer rate - is the difference between a fast hard drive and a slower one. Linear transfer rates will be similar for most contemporary 7200rpm drives.The 3TB model is a completely different design. It tests just over 15ms random access. This is typical of most hard drives, and as a result, it is quieter. I've included an image of the performance test I ran on both 3TB and 4TB models side by side, unfortunately Amazon has shrunk the image and it isn't legible. It was meant to show the 12ms vs 15ms difference between the models.I've also included an image of 2 performance tests solely on the 4TB PH3400U. One is a test across the disk's full capacity, the other is a test of a 2TB partition, which is sometimes the maximum that can be used on some setups.Read on if you want a longer explanation of how different the 3TB and 4TB models are.I've purchased one of the 3TB model and 2 of the 4TB model. Both of my 4TB drives were purchased from this listing in retail packaging. My 3TB was purchased as a bare drive but it's the same drive that comes in the PH3300U retail box.I've been using the 3TB drive for a bit over a year, and the 4TB drives for 3-5 months (bought at different times). I recently checked the SMART status on these drives and they are all working perfectly. This review will mostly focus on the 4TB model.First note - if you are using Windows XP 32-bit, the 4TB drive will not even be visible unless you use a utility like HDAT2 to artificially limit it's reported capacity to 2TB. I have tried this and it does work, but if you don't know how to do this, the easy answer is to stick with the 2TB model since that's all the space XP32 will allow you to utilize anyway. XP users should also look into the subject of sector alignment. I recommend using the utility "gparted" to partition the drive. Avoid using the built-in partitioning tool in XP, because it doesn't understand 4KB sector alignment and this can hurt the performance.Windows XP 64-bit can use the full capacity if you use GPT partitioning. However, XP64 cannot boot from a GPT drive. Therefore, under XP64 the only way to use this drive's full capacity is if you are not using it to boot the OS.With Windows 7+, you can use the full capacity, but you need to enable GPT partitioning. If your drive only shows 2TB of space (or less), it's not because of a drive fault, it is because of the MBR vs GPT issue. I don't know the procedure for Windows 7+, but there should be plenty of articles online that explain it.--This Amazon listing combines several capacities of drives under the same listing and combines their reviews together. There are actually at least 2 families of drives represented here which are very different, so mixing the reviews together can be misleading. I suggest you only pay attention to reviews for the same capacity drive that you are buying.Another point - Toshiba uses a different part number for their retail packaging than the model number that's actually on the drives themselves. Don't be surprised that the drive inside the box will not have a PH3... part number on it. I don't like this practice, because it leaves open the possibility that they could change the drives at a later date while keeping the same retail box number. But as of writing, it seems the drives inside the boxes have remained consistent for a given size.The 500GB, 1TB, 2TB, and 3TB drives are all the same basic drive model, just with different capacities. These have part numbers in the form of DT01ACAxxx, where the last 3 characters denote the size. DT01ACA300 for example is the 3TB model.The 500GB-3TB family of drives are a Hitachi design that Toshiba inherited when they purchased part of Hitachi's hard drive business. They are made in a former Hitachi plant which is now owned by Toshiba. They are quieter, desktop consumer oriented drives with moderate seek performance and low noise level. They have 1TB per platter (the 500GB version, no longer listed, uses one side of 1 platter). When I searched the serial number for my 3TB DT01ACA300, it showed a 3yr warranty in effect from the date of manufacture. These drives have not scaled beyond the 3 platter version with a max capacity of 3TB.Meanwhile, Toshiba needed something they could sell to consumers at 4TB+. To that end, they did something that I think might have been a stopgap measure, but a stopgap which is awesome for the consumer as long as you know what to expect.The 4TB and 5TB models are a completely different family of drive. These are made in the Philippines and are a Toshiba design, they did not come from the Hitachi purchase. (I do not know if this applies to the 6TB model)By all accounts, and my own experience twice, if you purchase the PH3400U, you will receive an MD04ACA400.I will be attaching a photo that shows the 3TB and 4TB drives next to each other. As you can see, they are totally unrelated models from completely different plants.The 4TB MD04ACA400/PH3400U drives are made in the Philippines - same location as Toshiba's "Enterprise" hard drives are made. They also appear to borrow the same casing and circuit boards. It is important to note that these 4TB drives have loud seek noises which some might find offensive, but they also have faster seek performance.I have seen documentation showing that the 4TB drive is built using 5x 800GB platters. 800GB platters have been common for a few years in enterprise drives which are optimized for fast seek performance and have long warranties. The 5TB drive is built using 5x 1TB platters. I believe it is a close relative of the 4TB drive, but I don't own a 5TB so I'll avoid saying much about it.Many people (including myself) have had a pleasant surprise when we looked up the warranty for our 4TB drive's serial number. Their computer seems to think that the 4TB drive has a (suspiciously Enterprise-like) warranty of 5yrs from manufacture, not 3yrs as advertised.Based on their physical characteristics, location of manufacture, warranty length, and the fast but noisy seek performance, I think the conclusion must be that these drives are a "consumerized" version of Toshiba's Enterprise level 4TB drives. As such, they are analogous to the Western Digital Black drives (of which most models are consumerized versions of WD "RE" drives).I think Toshiba should be marketing these drives accordingly, but they haven't done so. As a result, they are overlooked by performance enthusiasts, while at the same time they generate complaints from people who don't like the noise and didn't realize what they'd be getting.The 4TB Toshiba is a high performance drive with mechanicals that I believe were originally designed for their "Enterprise" drives. This has both positive and negative aspects. The negative is that these drives can make audible "grinding" noises at times of random access. The positive is that the drive is fast and it probably has very good build quality.When the heads on the 4TB model need to move to a different position of the disk, they do it quickly and loudly. This is great if you value performance and don't mind hearing some access noise now and then. You might even have fond memories of when all hard drives made this sound. However, many people aren't used to hearing that sound today and might not like it.If you use the 4TB drive for long linear transfers, such as playing videos, you won't hear the access noise. In that case, the heads don't need to jump around, they will be essentially stationary. But if you use the drive to boot an operating system, you will hear some "churning" as the drive heads quickly locate all the little files involved with an OS. Personally I like the sound, but some people won't so it needs to be pointed out. Don't install your operating system on the 4TB drive if you don't like hearing any noise. I think the 5TB will also sound and perform the same.The 3TB model is quiet though, and the smaller ones should be as well (as explained above, 3TB and smaller drives are a different drive family than the 4TB and above).I am attaching pictures of the 3TB and 4TB drives next to each other, so you can see that they are unrelated designs.I also attached a picture of a side by side benchmark comparison of both drives, but it isn't legible. The benchmark is from the linux utility "gnome-disks". It shows that the 3TB and 4TB drives' linear transfer rates are similar, but random access is much faster on the louder 4TB drive. Random access on the 3TB drive is still decent - it is competitive for a drive that does not make audible seek noises. For comparison, it still has faster access than a WD Blue 1TB WD10EZEX that I also have tested.The last 2 pictures are benchmarks of the 4TB drive alone. One was testing the entire drive, the other tests only the first 2TB, which is what you'll be limited to if you use traditional MBR partitioning.I consider the 4TB Toshiba to be a great bargain. It's analogous to a WD Black but at a much lower price. But make sure this is what you actually want before buying. If you want quietness, stick to the 3TB model or below.